Hopefully someday we'll have some kind of tricorder device that can identify disease processes by gas/scents/smells.
It can hasten the process of identifying these chemicals if people with such a sense of smell present themselves to researchers. To me that's the most important takeaway of this story. Unfortunately, most articles reporting on the story bury the lede as the fact that people can smell disease draws more attention than what they're smelling, and that researchers either didn't seriously consider there might be such a chemical indicator or didn't know where to start until they had access to a super smeller.
This sort of diagnostic approach isn't new. Once upon a time doctors would taste urine samples! It just fell out of favor because machine and chemical tests are more reliable and consistent. But if you're not drinking other people's pee on a regular basis, or running a large scale, shot gun experiment (like a super smeller spending decades learning scents), initial discovery of such markers can become more difficult.
"Ayurvedic physicians (5th/6th century BCE) first noted the sweet taste of diabetic urine, and called the condition madhumeha ("honey urine")." - https://en.wikipedia.org/wiki/History_of_diabetes
A more palatable way to diagnose diabetes is to check if your urine attracts ants and flies.
The closest I could find was mention of smelling urine to determine pregnancy, which apparently was/is rather reliable. The next best was mention of the surgeon John Hunter discussing the taste of semen, though the author "assumes... [Hunter] was tasting his own". (I wouldn't assume that considering his interests and research. Google Books texts of Hunter's publications contained page after page of discussion about the genital fluids of male cadavers, but after his brief mention of the taste of semen from a live donor he never quite goes where you're fearfully hoping! I didn't get there in my skimming--so much preamble for stuff everybody learns in Zoology and Physiology 101--but I presume he ended up reporting many important discoveries about male reproductive tissues and processes.)
I wish Google Books was as awesome today as it was 10 years ago. They expose only a tiny fraction of the material they once provided, even for pre-20th century material that couldn't possibly be under copyright. :(
 I wonder if they were inspiration, perhaps indirectly, for the wine aroma wheel created by the chemist Ann Noble at UC Davis.
Only ever happens with close female friends, but I’ve identified the smell from regular standing conversation distance away with friends I haven’t seen for weeks and don’t otherwise know their cycle.
I think I somewhere read, but unrelated to ovulating, that this was made by nature to find suitable partners. Probably that natural smell is intensified by ovulating.
edit: And to be honest: I never told anyone before that I sometimes sense this different smell and I'm not sure I should. Women could probably feel uncomfortable and think their smell is somehow "bad" when others can sense it. Not sure.
Asking the women whether your perception is true would likely have led nowhere as most women are not aware of their fertile phases.
Search keyword seems to be ‚copulins‘, but the area appears a bit underexplored. Lots of companies trying to sell snake oil. Lots of urban legends about mind control. Some girls do try using their natural perfume to their advantage though.
The thing about compatibility you mention is more related to the immune system I think, and mutual.
I have a tendency to associate with alternative types who are aware of their cycle and are happy to talk about it, and have confirmed my observation by asking on multiple occasions.
Our culture and schooling doesn't encourage the development of the subtle senses.
It's another example of what's lost working virtually.
It's not an advantage knowing why the person smells the way they do. Just what to do.
There are very strong relationships between couples and known smell genetics. (I think being different is good?)
It's an interesting question how deodorant has changed our genes.
The cherry on top of your out-of-this-world comment. Do you know and/or keep track of some of your friends' cycles ?
Love eggs for breakfast, though, so it's a tough life.
The sense does depend heavily on state of mind, and body, so sometimes I'd only notice when already drinking. Works better on people I know well.
Part of it is I don't think we realize how weird and sensitive smell is even for us. Imagine the world through the nose of a dog or bear.
I didn't know this until reading your comment. It does seem weird that the skin is so permeable, so I looked it up. At least in this case, it doesn't seem to have anything to do with permeable skin.
EDIT: It's mentioned in passing in the linked article: "For one experiment in Manchester, sebum samples were taken from the upper backs of test participants." Other sources are more clear about the relationship to sebaceous glands.
> ... However, when given a different (and for humans quite difficult) task—namely, classification of suspicious mammographic densities (masses)—the pigeons proved to be capable only of image memorization and were unable to successfully generalize when shown novel examples. ...
So many people were not able to tolerate the smells of our civilization that the result was widespread rioting and mass insanity, pretty much bringing down civilization.
How do you tell someone they should use more deodorant without upsetting them?
Is there anything you can do to reduce your sensitivity to bad odors when at the gym? (Serious question. Not a problem I've looked into before.)
Surgeons use peppermint concentrate.
None of us in the family can tolerate things like fresh paint, dry cleaner establishments, nail polish, and other chemical smells. My mother tended to avoid the "better living through chemistry" cleaning products popular in the 70's and 80's because they bothered her a lot. I, unfortunately, have developed extreme chemical sensitivity, so I'm on the extreme end of this.
FWIW, nobody on this side of my family has ever gotten cancer (knock on wood). I often wonder if our profound awareness of toxins is also protective, in that we completely avoid things that others would be comfortable working with on a daily basis.
There seems to be a "gut-brain axis" at work, to the point where some are starting to think the gut is the starting point.
We're seeing an increasing number of disorders -- psoriasis , lupus, schizophrenia, among others -- where there's an underlying connection to the gut microbiome and to inflammation in general caused by "pathobionts" .
I don’t know if it was the cancer I smelled or messed up chemistry due to the cancer. But the smell made me feel deep dread.
Related from earlier this year: https://news.ycombinator.com/item?id=19528250
The thought of her ability potentially leading to advances in disease diagnosis is a humbling reminder of how complex the human body really is. And that there is still more to know.
They also train them to find land mines.
“It is emphasized that no bioassay-guided study has led to the isolation of true human pheromones, a step that will elucidate specific functions to human chemical signals.” 
Or is it sufficient to be a "subconscious smell," signaling or otherwise?
It's useful to identify it early, but for the most part the early symptoms are mild.
Otherwise there is no way to distinguish between someone who never got cancer and someone who did but had the progression stop before it became a problem.